Technical Abstract:
We evaluated a water-soluble lignin-based adjuvant to provide ultraviolet protection for microbial insecticides when treatments were applied to field grown cabbage plants. Sodium lignate (PC1307) is a water-soluble powder that we modified by adding glycerol at 5% w/w and pressing the mixture through a screen to form granules. Forming these granules improved wetting and dissolution of the lignin when added to a spray tank. The adjuvant formulation included granular calcium chloride (>16 mesh) dry mixed at 30% w/w with the granules in an effort to autoencapsulate the insecticides by cross-linking the lignin as the spray residue dried on the plants. Microbial insecticides tested were Beauveria bassiana (BotaniGard® ES, 2.5 x 10(13) conidia/ha), Bacillus thuringensis (DiPel® DF, 1.1 kg product/Ha), and two baculoviruses (AfMNPV and AcMNPV in 50% w/w glycerol formulations, 2.5 x 10(12) occlusion bodies/ha). Microbial treatments were applied three times (on separate dates) with or without 3.1 kg/Ha adjuvant for a total of nine treatments (including an untreated control to 5 replications in a randomized complete block design. Insecticidal activity was evaluated based on mortality of Trichoplusia ni neonates fed on leaf samples collected 2, 7, 26, and 50 hours after application. The adjuvant effectively extended insecticidal activity of bacterial and baculovirus treatments, which act as stomach poisons. However, the adjuvant interfered with the contact activity of B. bassiana, observed as low insect morality for the 2-hour sample.